A permanent magnet is used in a wide range of fields such as various electronic products, small precision instruments, and automobiles, and is one of important electric and electronic materials. Following a recent request for reduction in size and increase in efficiency of those instruments, a high-performance permanent magnet is desired. In response to such request, a demand for the high-performance permanent magnet is rapidly grown in recent years.
Herein, the permanent magnet is roughly classified into a sintered magnet and a bond magnet. The bond magnet has following advantages that cannot be obtained by the sintered magnet. Recently, the demand for the bond magnet is rapidly increasing in various kinds of actuators, sensors, electronic parts. The advantages are:
(1) A thin complicated shape can easily be obtained.
(2) Cracking hardly occurs as compared with the sintered magnet.
(3) Mass-productivity is excellent.
The bond magnet having the above-mentioned advantages is further classified with respect to a molding method. That is, the molding method is classified into a compression molding method, an injection molding method, and an extrusion molding method. Among others, a manufacturing method using the compression molding method is a method using a ferrite-based, SmCo-based, or NdFeB-based magnetic alloy powder as magnetic alloy powder and including the steps of mixing a thermosetting resin or the like as a binder with the magnetic alloy powder, filling a resultant powder mixture in a mold, and carrying out compression molding. If the compression molding is performed in a magnetic field, a bond magnet having an anisotropy can be manufactured.
In the injection molding method and the extrusion molding method, a material obtained by hot-kneading the magnetic alloy powder and the thermosetting resin is injection-molded or extrusion-molded in a mold. If the molding is performed in a magnetic field, a bond magnet having an anisotropy can be manufactured.
In recent years, following reductions in size of various electronic products and small-sized precision instruments, actuators, sensors, and electronic parts are also required to be reduced in size. Therefore, a magnetic core used in the above-mentioned components is strongly requested to have a higher magnetic permeability in a greater superposed magnetic field. In a magnet incorporated and used in the above-mentioned components, a wide variety of designs in shapes and characteristics are adopted. Even in such a situation that a large reverse magnetic field is applied to the magnet at an operation point unfavorable as a magnet characteristic, for example, in case of a thin shape, a high reliability such as small deterioration in long-term demagnetization is required.
At the same time, the products and the instruments mentioned above are designed as space-saving products and are therefore disadvantageous in view of heat radiation. As a consequence, the magnet is used at a higher working environment temperature. Thus, even in such a situation that, in a high working environment temperature, a large reverse magnetic field is applied to the magnet at an operation point unfavorable as a magnet, a high reliability such as small deterioration in long-term demagnetization is required.
In recent years, a surface-mount-type coil is desired. For a core used in such a coil, an oxidation-resistant rare-earth magnet which is not deteriorated in characteristics under a reflow condition is essential and indispensable.
Against the background of the global environmental problem, hybrid automobiles are rapidly developed. The number of actuators, sensors, and electronic parts used in the automobiles is therefore increased. Accordingly, a wide variety of designs in shapes and characteristics are adopted also for those magnets used in the above-mentioned components. Therefore, a high reliability is required in a severer working environment. At the same time, a reduction in cost is strongly required.
As an electronic part using a permanent magnet, there is known a magnetic device constituting a magnetic circuit, i.e., a device including at least one of a magnetic core, a yoke, another permanent magnet, and a coil. The permanent magnet is inserted into at least one location in the magnetic circuit constituted by the magnetic device and applies a magnetic bias to the magnetic circuit. As a device of this type, an inductance element is described in, for example, Japanese Unexamined Patent Application Publication (JP-A) No. 2002-231540.
For example, a conventional magnetic device is manufactured in the following manner.
At first, as shown in FIG. 32(a), a sheet magnet 321 having a predetermined shape and a predetermined size is manufactured by a known method. Alternatively, a bond magnet is manufactured by the compression molding method, the injection molding method, or the extrusion molding method, mentioned above.
Next, as shown in FIG. 32(b), the sheet magnet 321 thus obtained is coupled to a pair of cores (E-shaped core 322 and I-shaped core 323) so that the sheet magnet is located in a magnetic gap of a magnetic circuit. At this time, for example, a thermosetting adhesive (not shown) is arranged between each of the cores 322 and 323 and the sheet magnet 321.
Finally, the adhesive is hardened. Thus, a magnetic device as shown in FIG. 32(c) is completed.
However, the above-mentioned method of manufacturing a bond magnet using the compression molding is disadvantageous in that, in an anisotropic magnet manufactured by applying a magnetic field during molding, magnetic field orientation of the alloy magnetic powder is poor.
Furthermore, in order to obtain a magnet having a high intrinsic coercive force and hardly demagnetized, a strong magnetic field is necessary during magnetization. However, in the above-mentioned conventional method of manufacturing a bond magnet, the magnetic alloy powder must be magnetized and oriented simultaneously with molding in the mold. For this reason, an excessive magnetic field must be applied to the obtained magnet. Therefore, a large coil is required to generate the magnetic field and a large-scale and complicated molding machine is required.
In addition, with respect to the demand for a wide variety of shapes mentioned above, the conventional molding method is disadvantageous in that a thin bond magnet having a thickness of about 0.5 mm can not be manufactured.
With respect to a magnetization pattern as one of such a wide variety of designs, for example, in radial magnetization in which a magnetic flux is generated in a radial direction in a disk-shaped (or a ring-shaped) magnet from the center of a circle towards an outer periphery, it is difficult to apply a high magnetization field in the above-mentioned radial direction. Even if an iron yoke having a high saturation magnetic flux density is used, the magnetization field has a limit of about 2 T. Therefore, it is impossible to industrially obtain a disk-shaped bond magnet using a magnetic powder having a high intrinsic coercive force.
The above-mentioned Japanese Unexamined Patent Application Publication No. 2002-231540 discloses that a permanent magnet inserted into at least one gap portion of a magnetic path of a magnetic core is magnetized in a magnetic path direction of the magnetic core to thereby obtain an inductance element applied with a magnetic bias. In this method, however, in order to magnetize the permanent magnet inserted into the inductance element, a magnetizer having a magnetization coil larger than the inductance element is necessary. Further, the permanent magnet inserted into the inductance element must be magnetized one by one. Therefore, the method is disadvantageous in facility investment and productivity.
Further, the conventional inductance element disclosed in Japanese Unexamined Patent Application Publication No. 2002-231540 has a problem. that, in the magnetic circuit comprising the ferrite core, the permanent magnet, and the yoke, it is difficult to decrease a gap interval between the permanent magnet and the ferrite core to thereby reduce a magnetic loss. In order to solve this problem, finishing accuracy of machining must be improved. This results in a disadvantage in cost.
As described above, in the method of manufacturing a bond magnet using the conventional method, a large-scale, complicated magnetization coil for orienting and magnetizing the magnetic alloy powder and a large-scale, complicated molding machine are required in order to obtain an alloy magnetic powder having a high intrinsic coercive force. This results in a problem in cost. Further, it is difficult to manufacture a thin bond magnet having a thickness of about 0.5 mm and using the magnetic alloy powder. As another disadvantage, it is difficult to perform magnetization in a complicated pattern such as in the radial direction in the disk-shaped magnet or the like using the magnetic alloy powder.
Therefore, it is a first technical object of this invention to provide a method of manufacturing a bond magnet having a high intrinsic coercive force, which method is capable of forming a desired shape such as a thin shape having a thickness of, for example, 0.5 mm or less without requiring a large-scale, complicated molding machine and a large-scale magnetization coil and which method is capable of performing magnetization in a complicated pattern such as in a radial direction or the like in a disk-shaped magnet or the like.
It is a second technical object of this invention, with respect to a magnetic device which includes at least one of a magnetic core, a yoke, a permanent magnet, and a coil and which has a bond magnet arranged at least one location in a magnetic circuit constituted by the device or outside the magnetic circuit, to provide a bond magnet manufacturing method and a device manufacturing method which are advantageous in facility investment and productivity without requiring a magnetizer having a magnetization coil larger than the device in order to magnetize the bond magnet and without requiring magnetization of the bond magnet arranged in the device one by one.
Therefore, it is an object of this invention to provide a bond magnet manufacturing method which is capable of easily and economically manufacturing a bond magnet having excellent magnetic characteristics, a magnetic device manufacturing method using the bond magnet manufacturing method and to provide an inexpensive bond magnet and an inexpensive device.